A transponder or “RFID Tag” is an electronic element comprising at least one chip connected to an antenna including a memory in which digital data is stored. The content of this memory can be consulted or read with the help of a suitable reader that transmits an electromagnetic signal intended to be picked up by the antenna of the transponder. This signal provides the energy necessary for the activation of the chip that returns to the reader, via the same antenna, a response signal containing the data stored in the memory of the chip.
Except the contactless chip cards, a conventional transponder application consists in integrating them into labels that can be stuck or attached to any object (goods in a store, spare parts in warehouse, luggage, etc.).
Thanks to their reduced thickness and in an aim to provide protection against counterfeiting, transponders can also be directly imbedded into the material forming the objects such as valuable documents, banks notes, compact discs, badges, cards etc.
When several transponders are fixed or inserted into an object, their reading can become more difficult because, being supplied simultaneously by the electromagnetic field of the reader, they also respond simultaneously. In order to distinguish the response of one transponder from that of another, it is necessary to isolate them electromagnetically by means of shielding elements.
The document U.S. Pat. No. 6,176,425 describes a system where a set of transponders located on an object is managed by a reader that is capable of sequentially picking up the data originating from each transponder. Said transponders have an individual reading zone in which it is possible to read the data stored in the transponder in question.
In order to select a given transponder, movable shielding elements placed in the vicinity of the transponder can be positioned in different ways. According to their position, these shielding elements allow either to direct the signal emitted by the antenna of the transponder in a given direction without overlapping into the reading area of another transponder, or to mask the transponders to let inactive during the reading of one transponder alone.
These shielding elements known in the form of electromagnetic conductive sheets have the capacity to absorb the electromagnetic energy transmitted by the reader in order to block the activation of the transponder chip. Embodiment examples of such sheets and their composition are described in the documents U.S. Pat. Nos. 4,774,148 and 6,344,155.